The detectors used in the conventional surveillance system are mostly of “active detection”, such as “visible light”, “infrared light”, “ultraviolet light” and the like, which belongs to “active” system and the layout of the surveillance system is very difficult. Monitoring the target using the characteristics of ultra-infrared light emitted by the target itself can reduce the complexity of the entire surveillance system. In case of poor penetration of visible light source, such as encountering smoke, haze, all black at night, only the ultra-infrared light (heat) can be detected, thus this technology can be widely applied to occasions, such as fire control, anti-theft at night and the like. Far-infrared monitoring typically involves the use of a temperature difference between the radiation source and the environment to find the monitoring target, therefore the infrared imaging capability and temperature resolution of the far-infrared system is very important.